A suspended ridge-type microstrip line planar slow wave structure

Abstract

The application discloses a suspended and ridged microstrip line planar slow wave structure, which is different from a conventional suspended microstrip line slow wave structure, and is characterized in that a periodic metal U-shaped zigzag microstrip line is suspended, and a metal ridge is additionally arranged on a straight section of the microstrip line, so that a dielectric substrate on which the periodic ridged metal zigzag microstrip line is printed mainly plays a supporting role, electromagnetic waves are mainly distributed in vacuum cavities on the upper and lower sides of the dielectric substrate, and a strong longitudinal electric field distribution is formed above the periodic metal zigzag microstrip line, because the metal ridge is arranged on the straight section of the microstrip line, so that a larger coupling impedance can be further obtained, and the interaction efficiency of a microstrip line planar traveling wave tube amplifier is finally improved. Taking a W-band U-shaped periodic suspended metal zigzag microstrip line slow wave structure as an example, the coupling impedance at 96 GHz is increased by 194% by adding the ridge to the U-shaped periodic suspended metal zigzag microstrip line.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microwave electric vacuum technology, and more particularly relates to a suspended ridge-type microstrip line planar slow wave structure. BACKGROUND

[0002] As an important microwave and millimeter wave power source, electric vacuum devices are widely used in the technical fields of communication, guidance, remote sensing, etc. Electric vacuum devices have the advantages of high power, high gain, high efficiency, high frequency and long service life, but solid-state power amplifier devices have the characteristics of small size, light weight and integration. With the rapid development of solid-state power amplifier devices towards high frequency and high power, they are posing a greater challenge to electric vacuum devices. How to ensure the advantages of electric vacuum devices while achieving miniaturization and low voltage to better adapt to the needs of technological development is an important development direction of microwave electric vacuum devices.

[0003] Microwave power modules combine the advantages of electric vacuum power amplifiers and solid-state power amplifier devices, and are very suitable for applications such as airborne systems and communication satellites that have strict requirements on device size and weight. At present, the electric vacuum power amplifiers in microwave power modules basically use spiral line traveling wave tubes. Spiral line traveling wave tubes have the advantages of wide frequency band, high efficiency and low voltage. However, at high frequencies (>65 GHz), the processing and assembly of spiral lines become very difficult. In addition, the spiral line slow wave structure is a three-dimensional structure, which is difficult to integrate with solid-state circuits. These factors limit the development of microwave power modules towards high frequency and integration.

[0004] Microstrip line planar traveling wave tube amplifiers have the advantages of small size, light weight and easy processing, and are one of the potential choices to replace spiral line traveling wave tubes in microwave power modules. Microstrip line planar traveling wave tube amplifiers use microstrip line slow wave structures as the interaction circuit. The microstrip line slow wave structure is a two-dimensional structure, which is easy to integrate with solid-state circuits; at high frequencies, the planar microstrip line slow wave structure is also easy to process using micro-fabrication processes such as MEMS. These advantages make the application prospect of microstrip line slow wave structure planar traveling wave tube amplifiers more promising.

[0005] However, the microstrip line slow wave structure also has some problems: the dielectric substrate is placed on the lower surface of the metal microstrip line, the electromagnetic wave transmitted by the microstrip line slow wave structure is a quasi-TEM wave, and the electromagnetic wave is mainly concentrated in the dielectric substrate; the electromagnetic field on the upper surface of the microstrip line exists in the form of surface wave, and the electromagnetic wave decays exponentially with distance away from the microstrip line. Therefore, the longitudinal electric field on the upper surface of the microstrip line slow wave structure is weak.

[0006] Coupling impedance is a parameter for evaluating whether the slow wave structure can effectively interact with the electron beam, and its calculation formula is as follows

[0007] Kc = Ezm^2 / 2*β^2*P

[0008] where Kc is the coupling impedance, Ezm is the longitudinal electric field amplitude at the location passed by the electron beam center, P is the power flow through the slow wave system, and β is the phase constant.

[0009] As can be seen from the above formula, the coupling impedance is low due to the weak longitudinal electric field in the conventional microstrip line slow wave structure, which eventually results in low interaction efficiency of the microstrip line planar traveling wave tube amplifier. SUMMARY

[0010] The present application aims to overcome the deficiencies of the prior art and provide a suspended and ridged microstrip line planar slow wave structure to effectively increase the longitudinal electric field amplitude of the microstrip line slow wave structure, thereby greatly improving the coupling impedance of the microstrip line slow wave structure, and also being easy to process.

[0011] To achieve the above-mentioned application purposes, the suspended and ridged microstrip line planar slow wave structure comprises a rectangular metal shielding cavity in vacuum, slots are opened on both sides of the center of the transmission direction inside the rectangular metal shielding cavity, and a dielectric substrate with a periodic metal meander microstrip line printed therein is embedded in the slot and placed in a suspended manner, thereby constituting a suspended microstrip line slow wave structure.

[0012] A single period of the periodic metal meander microstrip line is a U-shaped structure, i.e., a single period is composed of a semicircular microstrip line, a straight microstrip line extended from both ends of the semicircular microstrip line, and a quarter circular arc microstrip line with a radius equal to that of the semicircular microstrip line connected outward at the end of the extended straight microstrip line, so that the U-shaped structure is connected in sequence along the transmission direction to constitute the periodic metal meander microstrip line.

[0013] Characterized in that:

[0014] A metal ridge is added to the straight microstrip line part of the U-shaped structure, and the metal ridge is obtained by widening the straight microstrip line part of the U-shaped structure by a certain length before and after the midpoint.

[0015] The purpose of the present application is achieved in this way.

[0016] The present application is a suspended ridge type microstrip line planar slow wave structure, which is different from the conventional suspended microstrip line slow wave structure. The periodic metal U-shaped meander microstrip line is suspended, and a metal ridge is added to the straight section of the microstrip line. In this way, the dielectric substrate with a periodic ridge metal meander microstrip line printed on the surface mainly serves as a support, and electromagnetic waves are mainly distributed in the vacuum cavity on both sides of the dielectric substrate. Above the periodic metal meander microstrip line, there will be a strong longitudinal electric field distribution, because a metal ridge is added to the straight section of the microstrip line, so that a larger coupling impedance can be further obtained, and finally the interaction efficiency of the microstrip line planar traveling wave tube amplifier is improved. Taking a U-shaped periodic suspended metal meander microstrip line slow wave structure in the W waveband as an example, by adding a ridge to the U-shaped periodic suspended metal meander microstrip line, the coupling impedance at 96GHz is increased by 194%.

[0017] In addition, in order to make the ridge microstrip line slow wave structure have higher interaction efficiency, the microstrip line slow wave structure generally interacts with a ribbon-shaped electron beam with a large width-to-height ratio, and the ribbon-shaped electron beam needs to be as close as possible to the surface of the metal microstrip line, which makes the design of the focusing system of the planar traveling wave tube based on the microstrip line slow wave structure more difficult to implement in the actual tube manufacturing process. By using the suspended ridge method, a strong longitudinal electric field can be obtained at a position far from the surface of the microstrip line, so that even a circular electron beam can have a good interaction effect, thereby reducing the design difficulty of the focusing magnetic field of the microstrip line type planar traveling wave tube amplifier. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a single period structure schematic diagram of a specific embodiment of the suspended ridge type microstrip line planar slow wave structure of the present application;

[0019] Figure 2 is Figure 1 the side view schematic diagram of the single period structure;

[0020] Figure 3 is Figure 1 the top view schematic diagram of the dielectric substrate and the ridge metal meander microstrip line;

[0021] Figure 4 is a single period schematic diagram of a specific embodiment of the existing suspended microstrip line slow wave structure;

[0022] Figure 5 is Figure 4 the side view schematic diagram of the single period structure;

[0023] Figure 6 is Figure 4 the top view schematic diagram of the dielectric substrate and the ridge metal meander microstrip line;

[0024] Figure 7 isFigure 1 The microstrip line slow wave structure of the present application and the same size of the conventional suspended microstrip line slow wave structure are compared in terms of dispersion curves. Figure 4 The microstrip line slow wave structure of the present application and the same size of the conventional suspended microstrip line slow wave structure are compared in terms of coupling impedances.

[0025] Figure 8 The microstrip line slow wave structure of the present application and the same size of the conventional suspended microstrip line slow wave structure are compared in terms of dispersion curves. Figure 1 The microstrip line slow wave structure of the present application and the same size of the conventional suspended microstrip line slow wave structure are compared in terms of coupling impedances. Figure 4 The microstrip line slow wave structure of the present application and the same size of the conventional suspended microstrip line slow wave structure are compared in terms of dispersion curves. DETAILED DESCRIPTION

[0026] The specific embodiments of the present application will be described below with reference to the accompanying drawings so that those skilled in the art can better understand the present application. It should be noted that in the following description, when detailed descriptions of known functions and designs can obscure the gist of the present application, these descriptions will be omitted herein.

[0027] In the present application, a metal ridge is added to the straight microstrip line portion of the U-shaped structure, the metal ridge being obtained by widening the straight microstrip line portion of the U-shaped structure by a certain length before and after the midpoint of the straight microstrip line portion. In this way, the conventional periodic metal meander microstrip line is improved to a periodic ridge-added metal meander microstrip line.

[0028] Figure 1 is a single period diagram of the structure of a specific embodiment of the microstrip line slow wave structure of the present application.

[0029] In the present embodiment, as shown in Figure 1 The suspended ridge-added microstrip line planar slow wave structure of the present application includes a rectangular metal shielding cavity la and a dielectric substrate 3a on which a periodic ridge-added metal meander microstrip line 2a is printed.

[0030] The dielectric substrate 3a on which the periodic ridge-added metal meander microstrip line 2a is printed is inserted into the slot, i.e., the recess cl, on both sides of the center longitudinal direction (the transmission direction) inside the rectangular metal shielding cavity la, so that the periodic ridge-added metal meander microstrip line 2a is placed in a suspended manner, thereby constituting a suspended ridge-added microstrip line planar slow wave structure. An electron beam (not shown) passes from above the periodic ridge-added metal meander microstrip line 2a of the dielectric substrate 3a to achieve interaction with electromagnetic waves.

[0031] In the present embodiment, as shown in Figure 2 and Figure 3As shown, the size of the suspended ridge type microstrip line planar slow wave structure of the present application is as follows: the dielectric constant of the dielectric substrate 3a is ε, the thickness of the dielectric substrate 3a is y, the transverse length is x, the periodic length of the periodic ridge metal meander microstrip line 2a is p, the width is w, the thickness is t, l is the length of the straight section of the microstrip line, rid is the radius of the microstrip line, jx is the length of the ridge along the x direction, that is, a certain length before and after the midpoint of the straight microstrip line section, jz is the width of the ridge along the z direction, that is, half of the width after widening on both sides, the distance from the upper surface of the dielectric substrate to the height of the upper side in the rectangular metal shielding cavity is hs, the inner width of the rectangular metal shielding cavity is a, and b is the height of the metal shielding cavity.

[0032] In the present embodiment, the support medium is quartz, and the dielectric constant ε = 3.8. The specific structural parameter size is as follows (unit: mm): y = 0.128, x = 0.1, p = 0.12, w = 0.02, t = 0.02, l = 0.3, hs = 0.435, a = 0.7, b = 0.87, rid = 0.02, jx = 0.2, jz = 0.02. That is, in the present embodiment, the width of the ridge along the z direction is 0.04, which is twice the width of the metal meander microstrip line 0.02, that is, the width after widening on both sides is twice the width of the metal meander microstrip line.

[0033] The suspended ridge type microstrip line planar slow wave structure of the present application can be placed in the air by a single dielectric substrate, or can be placed in the air by two dielectric substrates in mirror image symmetry.

[0034] Figure 4 is a single period schematic diagram of a specific embodiment of the prior suspended microstrip line slow wave structure;

[0035] In the present embodiment, as shown in Figure 4 as a comparison, the suspended microstrip line slow wave structure also includes a rectangular metal shielding cavity 1b in vacuum and a dielectric substrate 3b on which a periodic metal meander microstrip line 2b is printed.

[0036] The dielectric substrate 3b on which the periodic metal meander microstrip line 2b is printed is embedded in the slot, that is, the recess c2, so that the periodic metal meander microstrip line 2b is placed in a suspended manner, thereby forming a suspended type microstrip line slow wave structure, and the electron beam (not shown) passes from above the periodic metal meander microstrip line 2b of the dielectric substrate 3b to realize interaction with electromagnetic waves.

[0037] Figure 5 is a structure side view schematic diagram of this specific embodiment of Figure 4 ;

[0038] Figure 6 is a structure side view schematic diagram of this specific embodiment of Figure 4a top view schematic diagram of the support medium and microstrip line structure of this embodiment;

[0039] In this embodiment, as shown in Figure 5 and Figure 6 , the dimensions of this microstrip line slow wave structure are as follows: the dielectric constant of the medium substrate 3b is ε, the thickness of the medium substrate 3b is y, the lateral length is x, the periodic length of the periodic metal meander microstrip line 2b is p, the width is w, the thickness is t, l is the length of the microstrip line straight section, rid is the radius of the microstrip line, the distance from the upper surface of the medium substrate to the upper side of the rectangular metal shielding cavity is hs, the inner width of the rectangular metal shielding cavity is a, and b is the height of the metal shielding cavity.

[0040] In this embodiment, the support medium is quartz, and the dielectric constant ε = 3.8. The specific structural parameter dimensions are as follows (unit: mm): y = 0.128, x = 0.1, p = 0.12, w = 0.02, t = 0.02, l = 0.3, hs = 0.435, a = 0.7, b = 0.87, and rid = 0.02.

[0041] In these two embodiments, Figure 1 and Figure 4 the difference between the two single-period microstrip line models is that one has a ridge and the other does not, and the remaining size parameters are consistent.

[0042] Using three-dimensional electromagnetic simulation software, the structure and dimensions shown in Figure 2 and Figure 3 , and Figure 5 and Figure 6 are used to simulate and calculate the microstrip line slow wave structure of the present application, and the high-frequency characteristic parameters are obtained, and compared with the same size Figure 4 This suspended non-ridged microstrip line slow wave structure is compared.

[0043] Figure 7 is Figure 1 the microstrip line slow wave structure of the present application and the same size Figure 4 The dispersion curve comparison chart of the existing suspended microstrip line slow wave structure;

[0044] In addition to using periodic metal microstrip lines, the metal layer printed on the medium substrate can also use other forms of planar structures. In this embodiment, as shown in Figure 4 , the microstrip line slow wave structure of the present application Figure 1 is deformed, and the periodic metal meander microstrip line 2b printed on the medium substrate 3b is replaced by a non-ridged form. From Figure 7In the figure, we can see that the dispersion curve of the microstrip line slow wave structure of the application is relatively steep, and the normalized phase velocity is relatively large. The suspended structure without a ridge has the characteristic of weak dispersion. After the structure with a ridge is suspended, by reasonably adjusting the parameters, the structure can be adjusted in a large range between weak dispersion and high coupling impedance, so as to meet the needs of various practical applications.

[0045] Figure 8 is Figure 1 In the figure, we can see that the dispersion curve of the microstrip line slow wave structure of the application is relatively steep, and the normalized phase velocity is relatively large. The suspended structure without a ridge has the characteristic of weak dispersion. After the structure with a ridge is suspended, by reasonably adjusting the parameters, the structure can be adjusted in a large range between weak dispersion and high coupling impedance, so as to meet the needs of various practical applications. Figure 4 The coupling impedance comparison chart of the existing suspended microstrip line slow wave structure;

[0046] From Figure 8 In the figure, we can see that the dispersion curve of the microstrip line slow wave structure of the application is relatively steep, and the normalized phase velocity is relatively large. The suspended structure without a ridge has the characteristic of weak dispersion. After the structure with a ridge is suspended, by reasonably adjusting the parameters, the structure can be adjusted in a large range between weak dispersion and high coupling impedance, so as to meet the needs of various practical applications. Figure 1 In the figure, the coupling impedance of the microstrip line slow wave structure of the application is greater than that of the conventional suspended microstrip line slow wave structure in the whole passband range. Figure 4 Taking 96GHz as an example, the coupling impedance of the conventional suspended microstrip line slow wave structure is 6.8 ohms, while the coupling impedance of the suspended microstrip line slow wave structure is 20 ohms, which is increased by 194%, which will greatly improve the interaction efficiency of the traveling wave tube.

[0047] Although the above describes the specific embodiments of the application for the purpose of facilitating the understanding of the application by those skilled in the art, it should be clear that the application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the application defined and determined by the appended claims, and all the application and creation utilizing the concept of the application are within the scope of protection.

Claims

1. A suspended ridge-type microstrip line planar slow-wave structure, comprising: A rectangular metal shielded cavity in a vacuum has slots on both sides of the center of the transmission direction inside the rectangular metal shielded cavity. A dielectric substrate with periodic metal zigzag microstrip lines printed on it is embedded in the slots and placed in a suspended manner, thereby forming a suspended microstrip line slow wave structure. The periodic metal zigzag microstrip line has a U-shaped structure for each cycle. That is, each cycle consists of a semicircular microstrip line, with a straight microstrip line extending from each end of the semicircular microstrip line. At the end of the extended straight line, a quarter-circle arc microstrip line with a radius equal to that of the semicircular microstrip line is connected outward. In this way, the U-shaped structure is connected sequentially along the transmission direction to form the periodic metal zigzag microstrip line. Its features are: A metal ridge is added to the straight microstrip section of the U-shaped structure. The metal ridge is a certain length before and after the midpoint of the straight microstrip section of the U-shaped structure, and the two sides are widened.

2. The suspended ridge-type microstrip planar slow-wave structure according to claim 1, characterized in that, The width after widening on both sides is twice the width of the metal zigzag microstrip line.

Images